One of the most active and challenging fields in molecular biology today is the genetic study of eukaryotic systems. An essential but often rate limiting step in this research is the screening of DNA libraries for gene isolation. In particular, imaging the distribution of radioactivity on the hybridization membrane typically requires 16 to 48 hours with standard autoradiography. A large area, real-time imaging system could dramatically improve the throughput of the DNA screening process. In Phase I of this program, we built a prototype instrument which imaged radiolabelled DNA transfer membranes in less than one hour in real-time. This was one hundred times faster than a comparable image of the same sample obtained with autoradiography. We also demonstrated the feasibility of constructing a large-area system which will image four primary screens with 0.6 mm spatial resolution in less than an hour. In Phase II we will conduct the research and development necessary to construct a fully functional prototype of this large area, real-time system for imaging radioactive DNA samples. Using this instrument, the researcher will be able to harvest pure genetic material without the delays of autoradiography and will be able to carry out the procedure with a much higher level of confidence. If this new instrument is made compatible with modern laboratory automation equipment, the entire process of identifying and selecting DNA clones could be automated.